1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a recording medium that is conveyed by a conveying mechanism.
2. Description of the Related Art
For example, Jpn. Pat. Appln. KOKAI Publication No. 2000-203009 discloses an image recording apparatus. FIG. 9 shows a configuration of the image recording apparatus of the Publication. Referring to FIG. 9, a recording means 31 includes recording heads 31C, 31M, 31Y and 31B of cyan C, magenta M, yellow Y and black B. A conveyor belt 32 is provided under the recording means 31. The conveyor belt 32 is pulled by four rollers 32a and moved by each of the rollers 32a. A recording medium P is placed on the conveyor belt 32. As the conveyor belt 32 moves, the recording medium P is conveyed to pass the recording heads 31C, 31M, 31Y and 31B in the order designated. If the recording medium P is conveyed in this direction, the recording head 31C is located upstream in the conveyance direction, while the recording head 31B is located downstream therein. When the recording medium P is conveyed under the recording heads 31C, 31M, 31Y and 31B, an image is formed on the recording medium P through the recording heads.
An adsorption roller 33 is provided the most upstream in the conveyance direction. A detection means is provided on the upstream side of the recording means 31. The detection means detects the rotation and displacement of a spur 34. The detection means includes an encoder plate, an optical sensor, a spur holder 35, a shaft 36 and a microswitch 38. The spur 34 has a number of teeth 34a that are projected from the rim thereof. The encoder plate is provided on the rotating shaft and rotates together with the spur 34. The optical sensor senses the encoder plate that is rotating. The spur holder 35 holds the spur 34 rotatably at one end and has a tensile spring 37 at the other end. The other end of the spur holder 35 is urged by the tensile spring 37. The shaft 36 swingably supports the spur holder 35. The microswitch 38 detects one of the ends of the spur holder 35.
With the above detection means, the adsorption roller 33 adsorbs the recording medium P on the conveyor belt 32. The teeth 34a of the spur 34 are brought into contact with the recording medium P by the urge of the tensile spring 37. Thus, the spur 34 rotates in response to the conveyance of the recording medium P. The encoder plate rotates together with the spur 34. The optical sensor senses the encoder plate that is rotating, and outputs an encoder pulse.
In response to the encoder pulse, the recording heads 31C, 31M, 31Y and.31B are controlled to jet out ink or the like. The ink jet out of these recording heads is laid on the recording medium P. Accordingly, an image is formed on the recording medium P.
While the recording medium P is moving, the optical sensor outputs encoder pulses at regular intervals. It is therefore determined that a trouble occurs in the conveyance of the recording medium P if no encoder pulses are output at regular intervals. Accordingly, the microswitch 38 detects a float or a jam of the recording medium P.